1. Field of the Invention
Halogenated isothiuronium salts are useful as flame retardants for polyurethane, polyester, and styrenic polymeric compositions.
2. Description of the Prior Art
During the past several years, a large number of flame retardants have been developed for use with an almost equally large number of flammable materials. Cellulosic materials such as paper and wood, and polymeric materials such as synthetic fibers and bulkier plastic articles are just two examples of the materials for which flame retardants have been developed. For any class of flammable materials, such as synthetic high polymers, those skilled in the art have long been aware that some flame retardant additives are more effective in polymers and polymeric compositions than other flame retardant additives. This is because the efficacy of any flame retardant in polymers or polymeric compositions is measured not only by the flame retarding capability of the additive but also by the ability of the additive to improve or modify, or at least not to detract from, other physical or mechanical properties of the polymer or polymeric composition. The mere fact, therefore, that most flame retardants contain halogen, phosphorus, and/or nitrogen atoms does not assure that any given halogenated or phosphorus or nitrogen-containing compound will impart useful flame retarding characteristics to all or even to any polymeric system. Furthermore, as those skilled in the art have improved the flame retardancy of many polymeric materials, they have been simultaneously required to provide the necessary flame retardancy with a minimal effect upon other properties of the polymers such as their light stability, processability and flexural, tensile and impact strengths. Balancing all of the foregoing considerations and thereby developing polymeric compositions with good flame retardant characteristics as well as a satisfactory balance of other properties is, consequently, a task which has in the past and presently continues to require the exercise of a high degree of inventive skill.
Previously it has been known that certain isothiuronium salts were useful in the control of plant growth, fungus, algae and the like. U.S. Pat. No. 2,640,079 discloses the use of alkylbenzylthiuronium salts as bactericides and fungicides. In U.S. Pat. No. 2,708,679 thiouronium pentachlorophenates are disclosed as useful herbicides. In a still later U.S. Pat. No. 3,513,197, S-benzylisothiuronium chlorides (as well as chloro and/or alkyl substituted) are useful as inhibiting algae. Finally, British Pat. No. 936,766 discloses that polychlorobenzyl mono- and bis-isothiuronium chlorides are useful as rodent repellents. It has now been found that certain bromophenyl isothiuronium salts are useful as flame retardants in polymeric compositions.